This invention relates to track-type vehicles and, in particular, to crawler vehicles having individually-driven sprocket wheels with separate transmission and torque convertors providing superior maneuverability and proven riding characteristics. Crawler dozers and loaders in current use in the construction industry are generally equipped with a single engine and transmission which drives a single pair of sprocket wheels through a final drive assembly which is ordinarily located at the rear portion of the vehicle. Each sprocket wheel has clutch and brake mechanisms incorporated into the final drive assembly, and with these control mechanisms, an operator drives and steers a set of continuous tracks or track chain assemblies on each side of the vehicle. For a quick turn, one track chain assembly is braked and the clutch employed while the track chain assembly on the opposite side remains moving. The degree of turn depends on the amount of braking and clutching action applied to the one side.
The track chain assemblies are usually tensioned by means of an idler wheel located at the front end of the continuous tread which generally exerts a constant resilient force on the idler wheel. Thus, when an obstacle is encountered, the track chain assembly can accommodate the obstacle while maintaining the same tension throughout. This resiliency of the track chain assembly reduces its wear and increases its maneuverability through all types of terrain.
On track-type vehicles, ground adhesion can be enhanced by the provision of pivoting means which are a part of the track chain assembly and aid in retaining maximum contact between the ground surface and the tread surface. The normal arrangement allows the track chain assembly to follow the ground regardless of its contour.
Although the above-described vehicles, in general use, satisfactorily perform and are in general acceptance at the present time, they all have some notable disadvantages in common; for instance, not only do the sprocket wheels provide for the driving power for the vehicle, but they also support a substantial portion of the total vehicle weight. As a direct result of this arrangement, not only the sprocket wheels, but the drive train and accessories, must have the capability of supporting the weight of the vehicle. They must also be able to withstand the stresses and strains associated with propelling such a heavy vehicle over such rough terrain.
Further, with the sprocket wheels being a part of the support structure of the vehicle, they must necessarily be directly on the ground, separated only by the tractor tread. This position subjects the sprocket wheel to a direct contact with whatever surface the vehicle may be traversing at the time, e.g., mud, rocks, sand and other abrasive materials. This direct contact of the sprocket wheels with these abrasive materials greatly accelerates the wear of critical parts on both the sprocket wheel and its associated supporting mechanisms. Thus, the general area of the final drive assembly and the track chain assemblies have often proven to be the weak point of the vehicle in respect to both down time and over-all maintenance costs. Since this general area of a track-type vehicle represents a substantial portion of the development and tooling costs of a new model and makes up a good portion of the total vehicle cost, an improvement obviating these difficulties is long-awaited in the industry.
Therefore, it is an object of this invention to limit the function of the sprocket wheels to propelling and maneuvering a track-type vehicle.
It is another object of this invention to position the sprocket wheels at an elevated distance from the ground, thereby minimizing contact with abrasive material.
It is yet another object of this invention to maintain maximum ground contact with the track chain assembly of track-type vehicles.
A further object of the present invention is a larger track-type vehicle with the utilization of multiple propulsion assemblies obtained from other models, well-proven in the field, with a minimum of development and expense.
Yet another object of the invention is to produce useful work while operating in either forward or reverse direction to a greater extent than by conventionally designed track-type vehicles.
These and other objects are attained in accordance with the present invention wherein there is provided a track-type vehicle having four individually-driven sprocket wheels providing power for the track chain assembly. The rotary motion of each sprocket wheel is controlled by a transmission and a torque convertor assembly which are adjacently mounted. A transversely-mounted engine powers each pair of sprocket wheels, one in the front and the other in the rear of the vehicle. Conventional transmission and steering mechanisms control the vehicle and, in conjunction, allow both sharp and regular pivotal turns while the vehicle is in motion. Each track chain assembly is resiliently and pivotally tensioned for a smooth ride no matter how rough the terrain.